Two-years static and dynamic monitoring of the Santa Maria di Collemaggio basilica

The Santa Maria di Collemaggio basilica is a 13th-century masonry masterpiece. The restoration works following the 2009 earthquake in L'Aquila included the installation of a permanent monitoring system. Crack gauges monitor a few significant cracks that appeared during the 2009 earthquake. Force-Balance accelerometers record the dynamic response of the entire structure. The dynamic response to ambient excitation leads to the estimation of the modal parameters. The current paper reports the outcomes of two years of static and dynamic monitoring from 1/1/2018 to 31/12/2019. The authors correlated the outdoor temperature and relative humidity to both the amplitude of the cracks and the modal parameters. The temperature deeply affects the static and dynamic response of the basilica. However, the linear correlations between the temperature and the structural response are diverse. There are cracks which stretch when the temperature rises and cracks which act oppositely. Natural frequencies lower when the temperature rises, while the same modes exhibit modal interaction phenomena. Furthermore, the natural frequencies of the basilica are not stationary but are moderately declining across the years. The basilica is a complex structure, where the different constitutive behaviour of three different materials, masonry, steel and timber may yield a varied structural response. The authors attempt to provide a qualitative interpretation of the observed behaviour, namely the detected correlations to the outdoor temperature, the lowering of the natural frequencies across the years and mode interaction phenomena.